[libFuzzer] Properly check if we can use dumpbin .

[mpividori]

Summary

The flag "/sumary" is necessary, otherwise it returns a non-zero value.

llvm/trunk/lib/Fuzzer/FuzzerUtilWindows.cpp

const void *SearchMemory(const void *Data, size_t DataLen, const void *Patt,
   for (const char *It = Cdata; It < End; ++It)
     if (It[0] == Cpatt[0] && memcmp(It, Cpatt, PattLen) == 0)
       return It;
 
   return NULL;
 }
 
 std::string DisassembleCmd(const std::string &FileName) {
-  if (ExecuteCommand("dumpbin > nul") == 0)
+  if (ExecuteCommand("dumpbin /summary > nul") == 0)
     return "dumpbin /disasm " + FileName;
   if (ExecuteCommand("llvm-objdump > nul") == 0)
     return "llvm-objdump -d " + FileName;
   Printf("libFuzzer: couldn't find tool to disassemble (dumpbin, "
       "llvm-objdump)\n");
   exit(1);
 }
 
 std::string SearchRegexCmd(const std::string &Regex) {
   return "findstr /r \"" + Regex + "\"";
 }
 
 } // namespace fuzzer
 
 #endif // LIBFUZZER_WINDOWS